Versatile Room‐Temperature‐Phosphorescent Materials Prepared from N‐Substituted Naphthalimides: Emission Enhancement and Chemical Conjugation

Abstract

Purely organic materials with room-temperature phosphorescence (RTP) are currently under intense investigation because of their potential applications in sensing, imaging, and displaying.I nspired by certain organometallic systems, where ligand-localized phosphorescence ( 3 p-p*) is mediated by ligand-to-metal or metal-to-ligand charge transfer (CT) states,wenow showthat donor-to-acceptor CT states from the same organic molecule can also mediate p-localized RTP. In the model system of N-substituted naphthalimides (NNIs), the relatively large energy gap between the NNI-localized 1 p-p* and 3 p-p*s tates of the aromatic ring can be bridged by intramolecular CT states when the NNI is chemically modified with an electron donor.T hese NNI-based RTP materials can be easily conjugated to both synthetic and natural macromolecules,whichc an be used for RTP microscopy.

Organic Nanocrystals with Bright Red Persistent Room‐Temperature Phosphorescence for Biological Applications

“…[4] In addition, the triplet states are easily quenched by atmospheric oxygen molecules through triplet-triplet energy transfer. [16][17][18][19] However, our ability to suppress the nonradiative processes of organic compounds remains limited. [5] Recently,r esearchers discovered several examples of pure organic materials that exhibited persistent phosphorescence in air and at room temperature.…”

“…[16][17][18][19] However, our ability to suppress the nonradiative processes of organic compounds remains limited. [18] This is because compounds with long-wavelength emission are generally needed to overcome the biosubstrate autofluorescence.I na ddition, as trategy should be available to control the crystal size to the nanometer range so that they [*] S. [16] Except for the crystallization approach, additional molecules or matrices are always involved in the rigidification methods, which add complexity to their applications with compromised performance owing to the diluted RTPm olecule concentration.…”

“…As such, intensely phosphorescent materials are largely known to exist in inert gases and at very low temperatures,w hich in turn limits their practical applications. [16][17][18][19] However, our ability to suppress the nonradiative processes of organic compounds remains limited. [6][7][8][9][10][11][12][13] These discoveries sparked several attempts to find ag eneral strategy to design more of such materials for various applications.Itwas found that to yield efficient RTP, several key factors have to be considered.…”

“…[20] So far,s everal strategies have been applied to minimize the intermolecular and intramolecular motions to activate the phosphorescence emission, which include hostguest doping systems with supramolecular gel entrapping, [21] metal-organic framework coordination [22] and rigid solid protection, [4] polymer assistance, [23,24] and crystal formation. [18] This is because compounds with long-wavelength emission are generally needed to overcome the biosubstrate autofluorescence.I na ddition, as trategy should be available to control the crystal size to the nanometer range so that they become compatible with biological systems.M oreover,t he obtained nanocrystals should remain emissive as the oxygen molecules dissolved in the aqueous media can effectively quench their phosphorescence.T his further requires the quantum yield of the RTPm olecules to be high enough so that they can remain emissive when they are well-dispersed in aqueous media. This is particularly ac oncern in biological applications because the biocompatibility and negligible interference between the matrix and the biosystem must be ensured, which adds further limitations to the design.…”

“…[14,15] To promote ISC and to favor pure organic RTP, heavy halogen atoms,a s well as organic groups with lone electron pairs,s uch as aromatic carbonyls,h ave been successfully introduced to organic compounds. [16][17][18][19] However, our ability to suppress the nonradiative processes of organic compounds remains limited. [20] So far,s everal strategies have been applied to minimize the intermolecular and intramolecular motions to activate the phosphorescence emission, which include hostguest doping systems with supramolecular gel entrapping, [21] metal-organic framework coordination [22] and rigid solid protection, [4] polymer assistance, [23,24] and crystal formation.…”